Antibiotic-resistant bacteria found in US wastewater treatment plants

Researchers have found methicillin-resistant Staphylococcus aureus (MRSA) in a significant number of wastewater samples taken from four US wastewater treatment plants.

"MRSA infections acquired outside of hospital settings - known as community-acquired MRSA or CA-MRSA - are on the rise and can be just as severe as hospital-acquired MRSA. However, we still do not fully understand the potential environmental sources of MRSA or how people in the community come in contact with this microorganism," commented study author Amy Sapkota (University of Maryland, USA) in a press statement.

"This was the first study to investigate US wastewater as a potential environmental reservoir of MRSA," she explained.

The team collected 44 samples of wastewater from four wastewater treatment plants - two in the mid-Atlantic region and two in the Midwest - to test for contamination with MRSA and methicillin-susceptible S. aureus (MSSA).

The samples were taken from different points of the treatment process, with 12 taken at the influent, five at the activated sludge reactor, three at the postaeration, four at the cell B, eight at the secondary clarifier, and 12 at the effluent stage.

In total, 22 (50%) samples were positive for MRSA and 24 (55%) for MSSA, the team reports in Environmental Health Perspectives. However, the chance of a sample being positive for MRSA decreased significantly as the treatment process progressed, with 83% of influent versus only 8% of effluent samples being positive for the bacteria.

Of the isolates sampled, 93% of MRSA and 29% of MSSA were resistant to multiple drugs.

"Our findings raise potential public health concerns for wastewater treatment plant workers and individuals exposed to reclaimed wastewater," co-author Rachel Rosenberg Goldstein, also from the University of Maryland, told the press.

"Because of increasing use of reclaimed wastewater, further research is needed to evaluate the risk of exposure to antibiotic-resistant bacteria in treated wastewater," she concluded.

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